Add headers-received event for extensions

[uwx]

Kindly squash this PR when merging, I'll fix the branch for next time

Sample of using the event:

moonlightHost.events.on('headers-received', (details: OnHeadersReceivedListenerDetails, isMainWindow: boolean) => {
    if (details.responseHeaders) {
        if(details.responseHeaders['X-Frame-Options']){
            delete details.responseHeaders['X-Frame-Options'];
        } else if(details.responseHeaders['x-frame-options']) {
            delete details.responseHeaders['x-frame-options'];
        }
    }
})

[uwx]

Gonna undo the generic EventEmitter because that seems to require a newer version of @types/node